A device for burning hydrogen-sulfide containing gas to produce process gas that contains hydrogen sulfide and sulfur dioxide for the Claus process is known from DE 34 30 015 C1, comprising a combustion chamber for generating the process gas at temperatures of 1000 to 1300° C., with tubes supplying air and hydrogen sulfide containing gas to the combustion chamber and with auxiliary firing in an auxiliary firing space merging into the combustion chamber, wherein the combustion gases of the auxiliary firing system are routed to the combustion chamber and the auxiliary firing system is provided with supply lines for hydrocarbon-rich heating gas, water vapor and air. At least one burner opens out into the combustion chamber, such burner being equipped with a central tube for oxygen supply, this central tube being coaxially surrounded by a second tube for supplying the feed gas that contains the hydrogen sulfide, and with an annular duct being arranged coaxially around the second tube for routing combustion air into the combustion chamber. This device enables feed gases with heavily fluctuating contents of hydrogen sulfide and heavily fluctuating feed gas rates to be processed. At extremely low hydrogen sulfide content, combustion takes place with pure oxygen, at extremely high hydrogen sulfur content, with air and under normal conditions, with air and oxygen.
In the Claus process, the feed gas containing the hydrogen sulfide is initially converted to a mixture of hydrogen sulfide and sulfur dioxide by partial combustion with the objective of adjusting a molar ratio of the two components of 2:1. The gas mixture thus obtained is converted to elemental sulfur and water in a catalytic Claus plant, and the offgas is fed to a desulfurizing facility. The offgas of the desulfurizing unit is typically modified to sulfur dioxide in a thermal post-combustion system so that an offgas forms which, however, only contains a small amount of sulfur dioxide.
In order to be able to process hydrogen-sulfide feed gas which also contains hydrocarbons and carbon dioxide, it is suggested pursuant to EP 0 315 225 B1 to feed the burner with gas which contains hydrogen sulfide as well as hydrocarbons or carbon dioxide, generating a temperature of 2000 to 3000° C. in the core zone of the burner flame and where a gas mixture of carbon monoxide and hydrogen is discharged from the combustion chamber at a temperature of up to 1650° C. Due to the high temperatures prevailing in the burner flame, most of the carbon dioxide contained in the feed gas is split into carbon monoxide and oxygen; water is partly decomposed to hydrogen and oxygen. In this way, part of the oxygen needed to maintain the high temperatures required in the flame zone of the burner and in the combustion chamber is made available so that the total oxygen demand can be kept low. The hydrogen existent in the product gas mixture of the combustion chamber is valuable for the downstream treatment of the gas mixture because hydrogenating reactions are thus viable without the addition of external hydrogen. Moreover, the gas components, hydrogen and carbon monoxide, can be used as synthesis gas.
When burning a feed gas stream containing hydrogen sulfide with pure oxygen exclusively, the outer annular duct is continuously purged with a small amount of air in order to prevent combustion gases leaving the combustion chamber from flowing back through the annular duct.
The mission of the present invention is to control the process described first in such a way that in the case of feed gas that contains hydrogen sulfide which can exclusively be burnt with pure oxygen, the supply of air via the external annular duct into the combustion chamber can be omitted.
The mission of the present invention is accomplished by purging the external annular duct with inert gas, preferably carbon dioxide, in order to suppress the reflux of combustion gases from the combustion chamber so that the combustion takes place with pure O2 (>90%) exclusively.
A beneficial aspect is that the carbon dioxide accumulating in gas scavenging processes, particularly the carbon dioxide obtained by desorption of laden methanol, can be used as purge gas.
An appropriate device for implementing the method features the arrangement of the burners in one or more circles surrounding the auxiliary firing space.